Conductive polymers originally attracted the attention of researchers over 20 years ago. The interest generated by these polymers compared to conventional conducting materials (e.g., metals) was largely due to factors such as light weight, flexibility, durability, and potential ease of processing. To date the most commercially successful conductive polymers are the polyanilines and polythiophenes, which are marketed under a variety of trade names.
More recently, conductive polymers have been used in the development of electroluminescent (EL) devices for use in light emissive displays. EL devices such as organic light emitting diodes (OLEDs) containing conductive polymers generally have the following configuration:                anode/buffer layer/EL polymer/cathodeThe anode is typically any material that has the ability to inject holes into the otherwise filled π-band of the semiconducting, EL polymer, such as, for example, indium/tin oxide (ITO). The anode is optionally supported on a glass or plastic substrate. The EL polymer is typically a conjugated semiconducting polymer such as poly(paraphenylenevinylene) or polyfluorene. The cathode is typically any material (such as, e.g., Ca or Ba) that has the ability to inject electrons into the otherwise empty π*-band of the semiconducting, EL polymer.        
The buffer layer is typically a conductive polymer and facilitates the injection of holes from the anode into the EL polymer layer. The buffer layer can also be called a hole-injection layer, a hole transport layer, or may be characterized as part of a bilayer anode. Typical conductive polymers employed as buffer layers are the emeraldine salt form of polyaniline (PANI) or a polymeric dioxythiophene doped with a sulfonic acid. The most widely used dioxythiophene is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, abbreviated as PEDT/PSS. PEDT/PSS is available commercially from Bayer, as Baytron® P.
PANI/PAAMPSA is typically prepared in aqueous solution by oxidative polymerization of aniline in the presence of PAAMPSA (see, e.g.,; Cao, Y., et. al., Polymer, 30, (1989) 2305; Armes, S. P., et. al., J. Chem. Soc., Chem. Comm. (1989) 88). JP5-262981 describes a high molecular weight PSS as a PANI dispersant. WO20014120 describes the use of PSS as a water-soluble host polymer.
Although PANI has been used successfully as the buffer layer in certain types of OLEDs, the low electrical resistivity typical of PANI inhibits its use in pixellated displays. For pixellated displays, a buffer layer having a higher resistance (i.e., lower conductivity) than is provided by PANI is desired to eliminate or minimize crosstalk between neighboring pixels. Inter-pixel current leakage significantly reduces power efficiency and limits both the resolution and clarity of the display. Thus, while the buffer layer must have some electrical conductivity in order to facilitate charge transfer, the conductivity of PANI buffer layers is generally higher than necessary and hence limits the resolution and clarity of the display in which PANI is used as the buffer layer. Accordingly, there is a need for high resistance PANI buffer layers for use in electroluminescent devices and for methods of increasing resistance of PANI buffer layers.